I found a blogger with a recipe:
This is our recipe. Put it on in the morning as soon as the dew is evaporated and any plant you put it on will be dead by evening. We use it in our driveway gravel, sidewalks, etc. Recipe: 1 gallon white vinegar, 2 cups epsom salts, 1/3 cup Dawn dishsoap (blue kind), mix and spray. It will kill any green growing plant
Hi Bennie - This is the most effective all-natural weed killer DIY that we use. It's even been featured on Hometalk! Hope this helps! Hugs, Holly
Mix 1 gallon of white vinegar with 1cup of table salt and a generous squirt of dawn liquid sink soap. Mix well in a watering can. Soak your weeds with mixture in the morning (preferably on a sunny day) and they will be quite dead by sundown. Repeat once a month so that any new weeds are stopped!